1. Field of the Invention
The present invention relates to an electronic component which operates with acoustic waves as an interdigital structure and/or "reflective array" arrangement having an input and an output transducer and with, under certain conditions, at least one reflector structure. At least one of the structures has at least one weighted region of the fingers of the structure.
2. Description of the Prior Art
Numerous embodiments of the electronic components are known from the prior art which operate with acoustic waves and which are employed as electrical frequency filters, signal generators, oscillators and the like. As a rule, these components have at least one input transducer and at least one output transducer which, depending upon the embodiment, can also coincide operationally to form one transducer. Such transducers can have the format of an interdigital structure including meshing electrode fingers.
Of significance are embodiments of such an electronic components which, in addition to the input transducer and the output transducer, also have one or more reflector structures which likewise comprise a respective multitude of fingers or, respectively, digit strips or, respectively, configurations corresponding thereto. There are "in-line" reflector structures (normal incidence) wherein 180.degree. reflection at the fingers occurs in the reflector structure. Other such reflector arrangements have two or more reflector structures disposed next to one another whereby the fingers of one reflector structure are disposed at an angle of approximately 90.degree. relative to the fingers of another reflector structure (oblique incidence).
An electronic component of the types set forth above can be dimensioned such that it executes a signal processing corresponding to a prescribed transfer function and emits the output signal corresponding to that function. Thereby dimensioned are the finger spacing and the weighting of the individual fingers, whereby a changing finger spacing is provided for filters having a dispersive property. As known, the mathematical determination of the required dimensioning is carried out by forming the Fourier transform of the transfer function. The Fourier transform is also referred to as the filter pulse response. It can be represented as a complex function EQU s(t)=a(t).multidot.e.sup.j[.omega. o.sup.t+.phi.(t)].
For a(t).noteq. constant, this function requires at least one weighted digital structure in the component. The weighting of a digit structure or, respectively, of the individual fingers of the structure is a designational reduction of the mechanical or, respectively, electro-mechanical efficiency of the fingers of the structure. Known in this regard for an interdigital structure is to have the mutually-adjacent electrode fingers situated at mutually-different potentials overlap one another to different degrees. Given high weighting, a topical overlap which is now only very slight occurs, this leading to disadvantageous wave diffractions.
In addition to the usually very disadvantageous measure of a more or less pronounced shortening of a respective finger, the measure also exists for reflector structures of replacing a finger (unweighted) designed as a through strip with a series of individual points (referred to as "dots") corresponding to the strip. The density and/or size of the "dots" dimensioned larger or smaller corresponds to a more or less shortened and, therefore, weighted finger (and such a respective structure replacing a finger is also referred to herein as a finger or digit strip). Disadvantageous in such an execution is that the "dots" cause noise signals due to the undesired reflection and scatter behavior (particularly given a higher weighting, i.e. a lower density of the "dots"). The original embodiment of weighted fingers in a reflector structure consists of realizing such fingers as grooves in the surface of the substrate and to make such a groove deeper or shallower corresponding to the weighting. This technology, in turn, has the disadvantage that it is extraordinarily expensive and is difficult to control.
In connection with the above, one may refer to the 1979 Ultrasonic Symposium Proceedings IEEE, pp. 696-700 of Chapman and of Kitano at pp. 585-589 of the same publication and 1976 Ultrasonic Symposium Proceedings IEEE, pp. 406-410 of Godfrey, all of which are fully incorporated herein by this reference.